{"record":{"id":"e3ce6808746f24b5","repo":"langchain-ai/langgraph","slug":"cannot-subscribe-to-channels-when-subscribed-to-a","errorCode":null,"errorMessage":"Cannot subscribe to channels when subscribed to a single channel","messagePattern":"Cannot subscribe to channels when subscribed to a single channel","errorType":"exception","errorClass":"ValueError","httpStatus":null,"severity":"error","filePath":"libs/langgraph/langgraph/pregel/main.py","lineNumber":277,"sourceCode":"        self,\n        *channels: str,\n        read: bool = True,\n    ) -> Self:\n        \"\"\"Add channels to subscribe to.\n\n        Node will be invoked when any of these channels are updated, with a dict of the\n        channel values as input.\n\n        Args:\n            channels: Channel name(s) to subscribe to\n            read: If `True`, the channels will be included in the input to the node.\n                Otherwise, they will trigger the node without being sent in input.\n\n        Returns:\n            Self for chaining\n        \"\"\"\n        if isinstance(self._channels, str):\n            raise ValueError(\n                \"Cannot subscribe to channels when subscribed to a single channel\"\n            )\n        if read:\n            if not self._channels:\n                self._channels = list(channels)\n            else:\n                self._channels.extend(channels)\n\n        if isinstance(channels, str):\n            self._triggers.append(channels)\n        else:\n            self._triggers.extend(channels)\n\n        return self\n\n    def read_from(\n        self,\n        *channels: str,","sourceCodeStart":259,"sourceCodeEnd":295,"githubUrl":"https://github.com/langchain-ai/langgraph/blob/38031739e551638e373fb553453256c23feeb41f/libs/langgraph/langgraph/pregel/main.py#L259-L295","documentation":"Error \"Cannot subscribe to channels when subscribed to a single channel\" thrown in langchain-ai/langgraph.","triggerScenarios":"Thrown at libs/langgraph/langgraph/pregel/main.py:277 when the library encounters an invalid state.","commonSituations":"See trigger scenarios.","solutions":[],"exampleFix":null,"handlingStrategy":null,"validationCode":null,"typeGuard":null,"tryCatchPattern":null,"preventionTips":[],"tags":[],"backgroundTag":null,"analyzedSha":"38031739e551638e373fb553453256c23feeb41f","analyzedAt":"2026-08-26T18:02:49.312Z","schemaVersion":2},"datasetVersion":"2026-08-26T21:11:00.512Z"}